The present invention relates, in general, to force indicators for medical or biological uses, and in particular, to a new and useful weight bearing indicator which is purely mechanical yet provides an unambiguous message, both tactile and audible, to a person wearing the indicator when two different amounts of force between the person's foot and the ground have been exceeded.
Following orthopedic surgery or injury to the lower extremities, patients are encouraged to gradually bear weight on their limb, but are warned not to exert more than a certain limited amount of force on the injured extremity.
As a result, most patients do not apply any weight or apply insufficient weight to the injured lower extremity in fear of causing further damage or pain. The application of weight is necessary, however, for proper recovery and not applying any weight is almost as detrimental as applying too much weight. A survey was conducted at Albany Medical College (Albany, N.Y.) involving over 100 patients. The patients indicated that often no weight was applied to the injured foot. Furthermore, a pilot clinical study was conducted on twenty bunionectomy patients who were given surgical sandals equipped with weight bearing indicator based on U.S. Pat. No. 6,405,606 (which will be discussed in greater detail later in this disclosure) and told to partial weight bear for a period of six weeks. Over two thirds of the patients that responded indicated that the device was useful for their recovery. Also see Walczyk, D. F., Bartlet, J. P., “An Inexpensive Weight Bearing Indicator Used for Rehabilitation of Patients with Lower Extremity Injuries,” Journal of Medical Devices, 2006.
Electronic devices are known which sense the force applied to a foot and provide a signal to the wearer. See, for example, U.S. Pat. No. 5,408,873 which discloses a foot force sensor and U.S. Pat. No. 5,357,696 which discloses a device for measuring force applied to a wearer's foot.
Additional relevant patents, are listed by patent number and title as follows:
Pat.No.Title of Invention6,122,846Force Monitoring Shoe6,031,463Load Signaling Device for a Patient's Foot5,619,186Foot Weight Alarm5,323,650System for Continuously Measuring Forces Applied to theFoot5,269,081Force Monitoring Shoe5,253,654Orthopedic Weight Monitor4,858,620Warning System for Excessive Orthopedic Pressures4,814,661Systems for Measurement and Analysis of Forces ExertedDuring Human Locomotion4,745,930Force Sensing Insole for Electro-Goniometer4,647,918Multi-event Notification System for Monitoring CriticalPressure Points on Persons with Diminished Sensation of theFoot3,974,491Load Signaling Device for a Patient's Foot3,791,375Device for Sensing and Warning of Excessive AmbulationForce3,702,999Partial Weight Bear Warning Device.
An electronic weight bearing alarm contained within a surgical shoe is also available under the trademark PEDALERT from Planet, LLC (Madison, Wis.). This device monitors the amount of weight a patient places on his or her lower limb through an advanced membrane sensor. An audible beep warning is generated when the weight limit is exceeded. A similar electronic device that can be placed in a patient's shoe is available under the trademark SANOSTEPPER from Sanostep, GmbH or Tauting, Germany.
Two patents of particular relevance since they use simple mechanical snap members to signal the wearer of the device and require no power and no complex mechanism, are U.S. Pat. No. 6,405,606, issued to one of the co-inventors of the present application (Walczyk) and another inventor in 2002 for Mechanical Weight Bearing Indicator for the Foot, and U.S. Pat. No. 6,752,028, issued in 2004 for Load Monitoring Test Device for a Patient's Foot. U.S. Pat. No. 6,405,606 is incorporated here by reference.
Neither of these patents disclose or suggest how, without power or complex mechanisms, two separate signals can be issued to the person wearing the device, which correspond to two different loads.
The need remains for a simple mechanical device which produces unmistakable feedback signals for a patient when two different loads are being applied to the patient's foot, so that the patient can be taught to exert a minimum desirable load on the foot during each step, but to avoid exerting more than a maximum desirable load.